JT65a computer programmer needed - an unusual app ?
3t3 at comcast.net
Sun Dec 23 11:00:41 CST 2012
I came across the request for help, listed below, on the Google Group's
What this chap is looking for seems to be something that some in AMRAD
would enjoy working on as a challenge.
I figured I would pass this on to our group to see if there are any of
us with adequate computer programing skills and/or background to be able
to advise Peter (VK3PB).
Peter's original request for help follows:
Hi all - I'm Peter Berrett VK3PB -
I was wondering whether someone could point me in the right direction
regarding JT-65 and programming.
I wish to build a wave propelled buoy that will float around in the
ocean and occasionally take pictures from cameras on its mast. I require
a communications system capable of achieving two ends (all on 20m).
1. The ability to send commands to the buoy in weak signal
conditions. Given the commands will be short I have concluded that JT-65
would be suitable. using abbreviations for the commands.
2. Send digital data back to me on request (5 watt transmitter on
- location (using a GPS)
- photos in JPG format up to 65KB
- other digital files as required.
Such transmission need to be reliable and over several thousand kilometers.
I have looked at a number of other modes and about the best I can find
is Olivia but JT-65 seems to have a 8 to 10db advantage over that e.g.
Olivia will do -10 to -14 db whereas JT-65 will do -22db.
Of course the problem is that JT-65 uses 200 hz to send 72 bits over 1
minute which is relatively slow.
What I would like to try and do is combine 10 JT-65 transmissions each
spaced at 200 hz intervals and send these in parallel and have them
simultaneously. Using SimJT I made 10 test files using 200 hz spacings
and -10b noise level. I then used Audacity to combine these into one
audio file and then played this into JT-65 HF. The program successfully
decoded all 10 transmissions thus showing that one could send 720 bits
in one minute. The combination of the noise in the 10 files made it
difficult to hear the tones but JT-65 HF worked flawlessly.
What I would like to do now is put together some software (linux based,
probably written in python) to
1. Take a digital file and chop it into different pieces each 72 bits in
2. Encode and combine 1 identification JT-HF transmission (72 bits) + 9
x 72 bits data transmission into an audio file
3. Play the combined audio file into my HF transmitter.
Similarly I would need to develop some software or a mechanism to
extract out the 72 bits from a JT-65 transmission received using JT-65 HF.
Needless to say the system I am proposing would be slow but could, over
a long period of time, send a JPG image reliably in very weak signal
My questions are
1. Is this the best way to solve my problem or is there another mode
which can reliably send a digital file over conditions where the signal
is 15db under the noise?
2. If not. What is the best programming language to use to put all
the above together? I am hoping that there are various libraries that
can be used to save me reinventing the wheel. One caveat however. I have
only previously programmed in BASIC so I will need to learn a new
language. Python would be my preferred option as I already own Head
First Python (teaching manual) and want to use a Raspberry Pi to send
and receive these transmissions.
Peter Berrett VK3PB
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3t3 at comcast.net
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